Kerckhoff's Prinzipien

1. The System must be practically, if not mathematically, indecipherable 2. It must not be required to be secret, 2. It must not be able to fall into the enemy without inconvenience 3. It's key must be communicable and retainable without the help of written notes 3. ... changeble or modifiable at the will of the corrisbondents 4. It must be applicable to telegraphic correspondence 5. It must be portable 5. Its usage and function must not be require the concourse of serveral people 6. Finally, it's necessary, given the circumstances that command its application, that the system must be easy to use, requiring neither mental strain nor the knowledge of long series of rules to observe